How to use it
Three pathways, one per tab:
- Interval: who needs surveillance, when it starts, and how often. Use the maximum extent ever documented, and the worst inflammation at the latest colonoscopy after optimised therapy.
- Dysplasia found: what to do next for visible, invisible or indefinite dysplasia, or a sporadic-type lesion.
- Pouch or rectum: surveillance after colectomy.
BSG 2025 risk tiers (Figure 3)
| Tier | Risk factors (any one) | Calculator 5-year aCRN risk | Plan |
|---|---|---|---|
| Population | None of those below | under 3.6% | Population screening; colonoscopic reassessment at 10 years |
| Small | Mild active inflammation; extensive colitis (UC proximal to the splenic flexure; Crohn’s over 50% or 3+ segments); post-inflammatory polyps; first-degree relative with CRC | 3.6–6.8% | Every 3 years |
| Moderate | Moderate active inflammation; PSC (from diagnosis); stricture or dysplasia in the last 5 years | 6.9–14.4% | Annual |
| Large | Severe active inflammation despite optimised therapy | 14.4% or more | Discuss colectomy |
Proctitis confirmed endoscopically, and Crohn’s disease that does not involve the colon above the rectum, need no IBD surveillance (2.1b). Everyone else has a baseline colonoscopy 8 years after symptom onset; PSC starts at diagnosis.
Healed left-sided colitis with no other risk factor falls into the population tier: BSG lists extent as a risk factor only when it is extensive.
Dysplasia (Figure 4)
- Visible and resectable: resect en bloc where possible. Unifocal polypoid LGD under 2 cm resected en bloc: colonoscopy at 12 months, then yearly for 5 years. All other dysplasia: at 3–6 months, then yearly for 5 years. Consider de-escalating after 5 clean years.
- Invisible (found in a random biopsy): MDT, second GI pathologist, optimise therapy, then a confirmatory colonoscopy within 3–6 months by a specialist IBD endoscopist with high-definition dye-spray chromoendoscopy and mapping biopsies. Only if invisible HGD or multifocal LGD is confirmed is colectomy the preferred option (urgent proctocolectomy discussion; 3–6-monthly surveillance if the patient declines).
- Indefinite: optimise therapy and repeat within 3–6 months; if re-confirmed, yearly until inflammation is controlled.
- Every dysplasia diagnosis gets double reporting and MDT discussion.
The calculator
The BSG-endorsed IBD aCRN risk tool (University of Oxford; checked online 8 October 2026) estimates the 5-year risk of advanced colorectal neoplasia (HGD or cancer) from 8 routine variables, using a dynamic model from 3731 patients in Canada, the Netherlands, the UK and the USA (Wijnands 2024). It applies to adults 18–75 with at least 30% of the colon involved and 7.5 or more years of disease (any duration with PSC). It does not cover a family history of CRC, colonic strictures, prior HGD or cancer, paediatric onset or familial cancer syndromes. If you enter its result, the tool shows both approaches and uses the shorter interval when they disagree.
How BSG differs from other guidance
ECCO (2023, restated unchanged in the 2025 ECCO-ESGAR-ESP-IBUS diagnostics and monitoring guideline) and the AGA 2021 update use intervals of 1, 2–3 or 5 years. BSG 2025 drops the 5-year interval: it judged 3 years the minimum effective interval and moved low-risk patients to population screening with a 10-year colonoscopic safety net. No Canadian (CAG) IBD surveillance guideline has been published since. This tool follows BSG 2025 throughout.
Technique. The guidelines also differ on how to look:
- BSG 2025 suggests HD dye-spray chromoendoscopy over other modalities (conditional, low certainty: a small gain in patients with dysplasia found over HD white light) and could make no recommendation on virtual chromoendoscopy.
- ECCO 2025 recommends HD chromoendoscopy, virtual or dye-based (EL3), with targeted biopsies, adding random biopsies in high-risk patients such as PSC.
- HELIOS (2025, 563 patients): HD white light with segmental re-inspection (a second look at each segment) was non-inferior to HD dye chromoendoscopy (neoplasia found in 10.3% vs 13.1%), suggesting much of dye spray’s benefit comes from the longer, more careful withdrawal.
The tool prints the BSG wording (dye spray). Where dye spray is not available, a careful HD examination with segmental re-inspection or virtual chromoendoscopy is a defensible alternative under ECCO; record which technique you used.
Pitfalls
- Surveillance in active disease is less reliable: optimise therapy first where you can.
- An inadequately prepared colonoscopy is not a good-quality negative examination.
- Re-assess risk after every examination; a flare or new stricture moves the patient up a tier.
- At 75, discuss whether to continue.
- IBD diagnosed before 18. BSG suggests considering surveillance every 1–3 years from transition to adult care (age 16–18), because the relative risk is high. The tool shows this note when onset before 18 can be inferred, and always on the “not yet due” result. The calculator does not cover paediatric-onset IBD.